The invention relates to a silver-ion-containing titanium oxide coating that has an alterable hydrophobicity, and a process for production thereof.
The tendency of a substance to mix with water is described by the hydrophilicity or its counter part, the hydrophoby. The extent of the hydrophoby of a surface is described by the hydrophobicity. A physical measure for the hydrophobicity of a surface is the contact angle, and DIN EN 828 describes how it is measured. At a contact angle of 0°, water forms a monomolecular film on the solid surface, while at a contact angle of 180° a drop of water only touches the solid surface in a point. At a small contact angle close to 0° there is strong interaction between the surface and the drop of water, the surface is termed hydrophilic. At contact angles around 90° and above the surfaces are hydrophobic ones and the wettability is very low here. In the case of even larger contact angles, the surfaces are called superhydrophobic, in the case of contact angles of approximately 160°, the term lotus effect is used.
The flow behavior of a flowing medium is also determined by the hydrophobicity of the surrounding vessel walls.
For a multiplicity of applications, for example medical implants as for example stents, microscale reactors, inside coatings of storage and reaction vessels, a precise and permanent setting of the hydrophoby/hydrophilicity is of great importance even in a very small space.
A hydrophobicity that can be set is of extreme importance, in particular in the area of medical technology, since on the one hand it shall be possible for body fluids to flow past without hindrance and in an optimum manner, on the other hand direct contact to the body tissue is present and it is desired that the implant grows on. Here the demand is therefore for a single implant to have quite different degrees of hydrophobicity. A particular advantage could be if the hydrophobicity can be matched exactly to the patient while inserting the implant. Subsequent structuring of materials/layers that are suitable for this purpose into neighboring hydrophobic/hydrophilic areas for application in microfluidics can further be used.
The choice of suitable carriers for a coating is limited as layers that have been applied must be cured by thermal treatment above 200° C. Not all carriers are suited for these temperatures.
The costs of a manufacturing process depend among others on the required energy and thus on the heating power necessary for carrying out the process, a reduction in the manufacturing temperature below 200° C. saves energy costs.
The publication “Titania and silver-titania composite films on glass-potent antimicrobial coatings” Page et. al.; J. Mater. Chem., 17, 95-104 likewise describes hydrophilic titanium-dioxide layers to which small amounts of silver ions have been added. Before being exposed, the layers have contact angles of 15° and no antimicrobial action; during exposure with UV light, a non-persistent (“persistent” can perhaps be replaced by “permanent”) antimicrobial action and a likewise non-persistent contact angle changing in the direction of super-hydrophilicity can be observed. A furnace having temperatures of 500 to 600° C. is used to produce the part-crystalline network.
Treating polymers by plasma, corona discharge and UV radiation for the purpose of manufacturing hydrophilic and hydrophobic surfaces are known from [M. R. Wertheimer, L. Martinu, E. M. Listen, J. Adhes. Sci. Technol., 1993, 7(10), 1091.], [D. Klee, R. V. Villari, H. Hocker, B. Dekker, C. Mittermayer, J. Mat. Sci.: Mat. Med. 1994, 5, 592.], [Y. I. Yoon, H. S. Moon, W. S. Lyoo, T. S. Lee, W. H. Park, J. Colloid Interface Sci. 2008, 320, 91] and [W. Xu, X. Liu, European Polymer J. 2003, 39, 199]. However, no persistent effect can be achieved.
The effect described here cannot be permanently achieved by a one-time irradiation of UV light, i.e. it is not persistent.
It is the object of the invention to provide a process for the production of a coating that can be permanently set to a persistent value in terms of its hydrophobicity by a single subsequent illumination.
It is a further object of the invention to provide a process for the production of a coating that can be permanently set to a persistent value in terms of its hydrophobicity even in the micrometer-scale range by a single subsequent illumination.
It is also the object of the invention to provide a process for the production of a coating that can be permanently set to a persistent value in terms of its hydrophobicity by a single subsequent illumination where temperatures of more than 200° C. are dispensed with.
Over and above this it is an object of the invention to provide a coating that can be set to a persistent value permanently in terms of its hydrophobicity even in the micrometer-scale range by a subsequent, single exposure.